It is to be understood at the outset that reference herein to an “enclosed” tank does not necessarily require that the tank headspace be a vacuum or that there is no means of access to inside the tank. It will become evident from a reading of this specification that the tank headspace need not be a vacuum and that an “enclosed” tank may well include within its scope a tank that includes an access port. Such a port may, during an aeration process, remain closed to avoid escape of odorous gases and to vent the tank above a roof line but at other times may be opened to allow partial or full access to inside the tank.
There exist a multitude of industrial applications requiring the use of an aeration tank for introducing compressed air into fluid held in the tank. One example is an MBBR tank which utilizes MBBR technology, a biological process used for wastewater treatment based on organisms/microbes attaching themselves to plastic bio-media (fixed film organisms). Most MBBR systems use aerobic processes which require the introduction of compressed air into liquor (a mixture of bio-media, treated water and introduced wastewater) held in the tank. The bio media grows a thin film of micro-organisms (biomass) on the surface of the plastic media which are kept in the tank by means of a screen on an outlet pipe of the tank which in turn allows fluid to exit the tank but not the plastic bio media. The large surface area of the plastic bio-media provides abundant surface area for microbial growth.
Wastewater enters the MBBR tank and the biomass attached to the surface of the bio-media degrades organic matter resulting in biochemical oxygen demand (BOD) removal and/or nitrification depending on the type and characteristic of the wastewater. The treated wastewater, containing some excess microbes which sloth off the media, may then flow through the screen to a downstream clarifier or dissolved air flotation system where the biomass and solids may be separated from the wastewater.
Most MBBR tanks are open top concrete or steel tanks or specially fabricated open top panel tanks. Air is typically compressed using blowers and transports the compressed air to the tanks via a series of pipelines from the top of the tank and then into diffusers positioned on the bottom of the tank. The diffusers are often coarse bubble diffusers with small holes drilled in the diffuser pipelines (also known as diffuser air manifolds). These air diffusers, which are typically constructed of expensive stainless steel, are either fixed to the floor of the tank or, depending on the size of the floor, are held down by their rigidity and weight to overcome the buoyancy effect of the displaced water. Coarse bubble diffusers uniformly placed at the bottom of the tank maintain the necessary level of dissolved oxygen (DO) concentration for BOD removal or nitrification.
In an MBBR tank, the holes in the diffuser pipelines can accumulate growth which causes blockages, or foreign objects can lodge in the diffuser pipeline holes. If the diffusers blocks, break or corrode, the diffusers need to be removed from the tank and this generally requires the liquor to be drained from the tank and the bio-media removed. This can be a time consuming process and the treatment process must be halted for an extended period of time to allow for cleaning and/or maintenance of the MBBR tank diffusers. Generally the tanks need to be completely drained and a substantial proportion of the bio-media needs to be removed to allow access to the air pipelines and diffusers. This can take a number of days at considerable cost. In addition, while the cleaning or repairs are taking place the treatment plant is not available to treat the wastewater, which in turn may lead to failure to comply with environmental discharge standards for the treated effluent.
In addition, because the top of the MBBR tank is open, the tank contents are open to atmosphere and therefore the spent air cannot be collected and vented to atmosphere via a vent pipe or passed through an odour scrubber or like equipment used to remove any odourous gases, if present, from the spent air. In addition, many MBBR tanks need to be installed in enclosed buildings to shield the appearance from neighbours, protect the system from the environment or to abate noise levels. It is therefore often desirable to collect the spent air and vent it separately via a vent pipe directly to atmosphere outside the building to prevent excessive humidification inside the building and/or to emit potential odorous gases from inside the building. Attempting to un-cover and re-cover a conventional MBBR tank with conventional diffusers for every cleaning or repair process is an extremely complex process and can incur considerable capital costs and ongoing operating costs if required to be removed during maintenance periods.
Accordingly, there is a need for an aeration assembly or an aeration tank incorporating same that allows for the removal of aerating diffuser(s) for the purpose of cleaning and/or maintenance of the diffuser(s) without needing to drain the tank or stop the aeration process. In the case of MBBR tanks, the tanks are also filled with bio-media which makes the tanks more difficult to drain and empty. In addition, the aerating diffusers are more prone to damage or becoming blocked and therefore require more regular cleaning. In the case of aeration processes which produce spent air with high humidity or which produce unpleasant odours, there is a need for an enclosed aeration tank which, in view of tank being covered, also allows for the removal of aerating diffusers from an exterior location.
It is an object of the present invention to overcome at least some of the aforementioned problems or to provide the public with a useful alternative.